System and method for detecting fibre tracts

ABSTRACT

The invention relates to a system for displaying fibre tracts of a human or animal, comprising memory means holding diffusion images of a region of interest of said human or animal, processing means connected to the memory means for deriving fibre tract data from the diffusion images, and display means for displaying the fibre tracts derived by the processing means wherein the processing means include a discriminator to select the fibre tract data to be displayed on the display means.

The invention relates to a system for detecting fibre tracts of a humanor animal, comprising memory means for holding diffusion images of aregion of interest of said human or animal, first processing meansconnected to the memory means for deriving fibre tract data from thediffusion images, and second processing means for processing the fibretracts derived by the first processing means.

Such a system is known from JP-A-11-000320.

In this known system the first processing means deduce a highestdirection of a diffusion coefficient with a pre-determined point as astarting point using a diffusion tensor at each point of the image anddeducing the next point located at a position that is a pre-determineddistance apart in that direction, and continuing this process with adeduced next point as the starting point for the next step. The displaymeans of this system serve as the second processing means of the fibretracks and merely display all points derived by this known method,resulting in an image which is considered to represent the nerve fibresthat are actually present.

A problem with this known system is that the displayed information isnot entirely accurate due to noise or other causes which results in thedisplay of fibres that are spurious or otherwise of no interest.

In this connection it is remarked that the diffusion images are theresult of indirect measurements such as obtained by magnetic resonanceimaging.

Magnetic resonance imaging is known in the art in general. Theapplication of magnetic resonance imaging for fibre tracking is knownfrom WO-A-01/91639.

From this publication WO-A-01/91639 it is known to initiate fibretracking by selecting a pixel from a diffusion tensor magnetic resonanceimage, to connect the pixels and to effect a judgement regardingtermination of the pixel tracking, which in each direction is based uponthe randomness of the fibre orientation of the adjacent pixels. Thetechnology disclosed in this document suffers however from the sameproblem as JP-A-11-000320, i.e. the processing or display of spuriousfibres.

The invention is aimed to resolve this problem.

According to the invention the system for detecting fibre tracts of ahuman or animal is characterized in that the first processing meansincludes a discriminator to select the fibre tract data to be processedby the second processing means. The second processing means can be usedfor several purposes, for instance to execute statistical analysis onthe data, or to effect that the fibre tract data are displayed ondisplay means.

By the application of the discriminator the validity of the fibre tractdata can be vastly improved.

This can particularly be accomplished in a system which according to apreferred embodiment is characterized in that the discriminator preventsselecting fibre tract data that jointly represent a fibre tract or fibretracts of less than a pre-determined length. The discriminator regardsfibre tracts of less than the pre-determined length as being invalid.Such too short fibre tracts are considered to be spurious whichconsequently need not be available for further processing such asdisplaying.

In a further aspect of the invention the system is characterized in thatthe discriminator prevents selecting fibre tract data that jointlyrepresent a bundle of fibre tracts of less than a pre-determined numberof fibre tracts per surface area or per volume. This measure rules outthe display of single erroneous tracts.

The invention is also embodied in a method of detecting fibre tracts ofa human or animal in which diffusion image data of a region of interestof such human or animal are processed to derive fibre tract data thatare thereafter further processed, for instance displayed.

The method of the invention is characterized in that further processingof the fibre tract data is restricted to such fibre tract data thatjointly represent a fibre tract or fibre tracts that satisfy at leastone predetermined criterion.

In a first preferred embodiment of the invention the method ischaracterized in that a first pre-determined criterion is selected torepresent a minimum-length of the fibre tract or fibre tracts.

In a second preferred embodiment which may be combined with the firstpreferred embodiment, the method is characterized in that a secondpre-determined criterion is selected to represent a minimum number offibre tracts per surface area or volume that are part of a bundle offibre tracts.

When indeed the first pre-determined criterion and the secondpre-determined criterion are employed in combination, the method mayautomatically yield all fibre bundles in the tissue being examined. Thistissue under examination may furthermore be compared to a standard dataset in order to improve the reliability of the fibre tracking accordingto the invention.

Results of the invention are shown hereafter with reference to anexemplary embodiment of a system according to the invention, in whichdiffusion tensor magnetic resonance images are processed in order toobtain fibre tracts. The invention further relates to a computerprogramme as defined in claim 7. The computer programme of the inventionmay be downloaded into a system for detecting fibre tracks so as toenable the system to carry out the method of the invention. The computerprogramme may be supplied on a data carrier such as a CD-rom, or may bedownloaded from a data network, such as the world-wide web.

FIG. 1 shows the system according to the invention.

FIGS. 2 to 5 show some results obtained with the system according to theinvention.

With reference to FIG. 1 the system according to the invention isindicated with reference number 1. This system for detecting fibretracts of a human or animal comprises memory means (2) for holdingdiffusion images of a region of interest of said human or animal. Theimages can be derived for instance with magnetic resonance imaging whichis known to the person skilled in the art and which requires thereforeno further elucidation.

The memory means (2) are connected to first processing means (3) whichoperates on the diffusion images that are held in the memory means (2).The first processing means (3) are connected to second processing means,in this example display means (4) for displaying the fibre tracts thatare derived from the diffusion images by the first processing means (3).To this end the first processing means (3) includes a discriminator toselect the fibre tract data that are to be displayed on the displaymeans (4). The results are comparatively shown in the following figures.

FIG. 2 shows the image visualised on the display when the discriminatoris not employed.

FIGS. 3, 4 and 5 show the image being visualised on the display meanswhen the discriminator is active to display only fibre tract data thatrepresent a minimum-length of the fibre tract or fibre tracts to bedisplayed.

In FIG. 3 the minimum-length of the fibre tracts to be displayed amountsto 10 voxels.

In FIG. 4 the said minimum-length amounts to 20 voxels whereas in FIG. 5the said minimum-length amounts to 30 voxels.

As a result of the invention the display of undesired short fibres isprevented and the recognition of bundles of fibres can take place moreeasy.

1. System for detecting fibre tracts of a human or animal, comprisingmemory means for holding diffusion images of a region of interest ofsaid human or animal, first processing means connected to the memorymeans for deriving fibre tract data from the diffusion images, andsecond processing means for processing the fibre tracts derived by thefirst processing means, wherein the first processing means includes adiscriminator to select the fibre tract data to be processed by thesecond processing means.
 2. System according to claim 1, wherein thediscriminator prevents selecting fibre tract data that jointly representa fibre tract or fibre tracts of less than a pre-determined length. 3.System according to claim 1, wherein the discriminator preventsselecting fibre tract data that jointly represent a bundle of fibretracts of less than a pre-determined number of fibre tracts per surfacearea or per volume.
 4. Method of detecting fibre tracts of a human oranimal comprising the steps of processing diffusion image data of aregion of interest of said human or animal to derive fibre tract data;processing the fibre tract data wherein processing the fibre tract datais restricted to such fibre tract data that jointly represent a fibretract or fibre tracts that satisfy at least one pre-determinedcriterion.
 5. Method according to claim 4, wherein a firstpre-determined criterion is selected to represent a minimum-length ofthe fibre tract or fibre tracts.
 6. Method according to claim 4, whereina second pre-determined criterion is selected to represent a minimumnumber of fibre tracts per surface area or volume that are part of abundle of fibre tracts to be processed.
 7. Computer programme fordetecting fibre tracts of a human or animal comprising instructions forprocessing diffusion image data of a region of interest of said human oranimal to derive fibre tract data; processing the fibre tract datawherein processing the fibre tract data is restricted to such fibretract data that jointly represent a fibre tract or fibre tracts thatsatisfy at least one pre-determined criterion.